Polarized Normal-Incidence Cavity Ring-Down Spectroscopy

Polarized Normal-Incidence Cavity Ring-Down Spectroscopy: Probing Spiropyran Photochromism in Thin PMMA Films and Toluene


A normal-incidence geometry, polarization-resolved cavity ring-down spectroscopy technique (polarized NICRDS) is described to probe the polarized absorbance of surface-adsorbed thin films and short-path length liquid samples. The technique is demonstrated by a kinetic study of the photochromic behavior of the spiropyran dye 6,8-dibromo-1′, 3′-dihydro-1′, 3′, 3′-trimethylspiro[2H-1-benzopyran-2, 2′-(2H)-indole]. The technique is shown potentially to have monolayer coverage sensitivity and can measure the angular orientation distribution of analyte molecules. The photochromic kinetics of 6,8-dibromoBIPS in toluene solution were qualitatively consistent with a previous study of this molecule using conventional absorption spectroscopy. The absorption polarizations and slow ring-closing kinetics measured in a thin poly(methyl methacrylate) film are consistent with a strong interaction of the spiropyran and merocyanine forms with the polymer matrix.

In the Journal of Physical Chemistry A.